RF communications exist. These communications incorporate portable communication units ("portables") that are powered by rechargeable batteries to enable communications in various locations without requiring an external power supply. Unfortunately, after several hours of use, the battery discharges and must be recharged or replaced with a charged battery.
Several techniques for providing a battery-saving system for portables are known. One such system employs a push-to-talk (PTT) circuit wherein the transmitter of the portable is manually keyed by a push button or the like when it is desired to transmit a message, the transmitter normally being unkeyed when no message is being transmitted. Full-duplex systems may utilize voice activation circuits to key the transmitter only while the user is speaking. Other systems apply synchronization codes and tone codes to enable the unit to operate in a low-power consumption mode when not engaged in a call.
In full-duplex cellular systems, cellular telephones adjust their transmit power level continuously in response to commands from the infrastructure. By reducing the transmitter whenever possible in this way, battery charge is conserved. These power-level commands are received on a separate dedicated supervisory channel. In many conventional communications systems, communication channels are a sparse commodity, and the use of a dedicated channel to convey power-level commands is too expensive a price to pay for battery savings in a portable.
Accordingly, a method of providing battery savings that extends battery usage time in a portable unit without use of an additional channel is desired.